There is an increasing need for sensor-driven lighting control systems having integrated sensors (presence, motion, motion-object-type, etc.) in lighting installations for smart light control, because of their advantage of bringing down the energy consumption of the light source(s) thereof, and thereby improving cost-savings, and life-time of the light source(s).
A range of sensing functionalities are being integrated in light poles, ranging from presence sensing (for light-control), orientation sensing (luminaire diagnostics) to environmental monitoring. Presence sensing allows light source(s) of a lighting system to be switched off or dimmed down when no persons or objects are present in a space, and conversely to be switched on or dimmed up when a person or an object is present in the space, to reduce the energy consumption of the lighting system. Orientation sensing allows sub-optimal orientation of a sensor to be detected which can be caused by poor installation of the sensor by a novice installer, and/or sometimes even after installation of the sensor due to a drift in its orientation due to mechanical or environmental effects, to be corrected and/or taking into account when controlling the light source(s).
The light source(s) are typically Light-Emitting Diodes (LEDs) due to the fact that LEDs consume less electrical energy than many conventional light sources such as conventional incandescent lamps, fluorescent lamps, neon tubes etc. and have much longer lifetimes. LEDs are vulnerable to damage if exposed to high temperatures and/or high humidity. Environmental monitoring enables environmental conditions such temperature and humidity to be monitored and used to avoid malfunction of the LEDSs i.e. turn off the LEDs or activate a cooling device such as a fan. Furthermore controlling the hue of the light emitted by the light source(s) is sometimes desirable as the environment changes, for instance when fog comes in etc.
Various precipitation sensing techniques are known, including a tipping-bucket rain gauge, an optical (infra-red) rain gauge (commonly used in automotive windshields), a capacitive sensor, and an acoustic rain sensor described in UK patent application publication no. GB2412735, whereby a microphone housed entirely within an enclosure is used to detect precipitation landing on an outer surface of the enclosure.